Production of nickel sulfamate

ABSTRACT

A process for preparing nickel sulfamate by dissolution of nickel powder in aqueous sulfamic acid solution. Very rapid nickel dissolution rate is obtained by oxygenating a suspension of nickel powder in sulfamic acid solution with substantially pure oxygen gas while controlling the pH of the system below about 5.0.

I United States Patent [111 3,620,669

[72] Inventors Nicolas ZubryckyJ [5| Int. Cl C01b 17/98 Fortsukatchewan; [50] Field oESeaI-ch 23/114 David John Ivor Evans, Edmonton, both of M c [56] References Cited [21] Appl. No. 834,583 UNITED STATES PATENTS 1 Flled Jul!e 2, 1969 3,321.273 5/1967 Fischer 23/114 [45] Patented Nov. 16, 1971 [73] Assignee Shel-rm Gordo Ming Llmjt d Primary Examiner-Earl C. Thomas Tom, om Cm Attorney- Frank I. Piper Continuation of application Ser. No.

416,818, Dec. 8, 1964, now abandoned. This application June 2, 1969, Ser. No. 834,583

[541 PRODUCTION OF NICKEL SULFAMATE 1 Claim, 3 Drawing Figs.

95 SULPHAMIC ACID CONSUMED ABSTRACT: A process for preparing nickel sulfamate by dissolution of nickel powder in aqueous sulfamic acid solution. Very rapid nickel dissolution rate is obtained by oxygenating a suspension of nickel powder in sulfamic acid solution with substantially pure oxygen gas while controlling the pH of the system below about 5.0.

AGITA T ION AND 45 RAT ION TAT ONL Y c PH I 2 3 6 DISSOLUTION TIME (HOURS) PATENTEnauv 16 IS?! 3 SULPHAH/C ACID $3 SULPHAHIC ACID CONSUMER CONSUMEO 75 SULPHAMIC ACID CONSUMED AGITAIION 90 AND 80 AERATION 70 TAT 60 omv c 30 3 F I G. I

I 2 3 l DISSOLUTION rm: (nouns NICKEL I N a 100 POWDER 80 A) v w /f NICKEL x105 FIG. 2 ,0 77.3. .3. M

orssownou nus (HRS) m V 3. VA

1 7 90 A J 00 ,i FIG. 3

60 h pH 3/ 50 Via/m 4o 4 J H ,.3 r h 2 M I 40 5070 -90 mo 02 a J 4 l 1 1 I 0.5 1.5 2 2.5 3 3.5 4 4.5 5 5.5 s 6.5

DISSOLUYION TIME (HRS) I NV! 5N! (IRS NICOLAS ZUfJR VL'A )1! A gem! PRODUCTION OF NICKEL SULFAMA'I'E This application is a continuation of application, Ser. No. 416,818 filed Dec. 8,1964 and now abandoned.

This invention relates to the preparation of nickel sulfamate and, more particularly, to a method of preparing nickel sulfamate by the rapid dissolution of nickel powder in aqueous sulfamic acid solution.

it is customary to produce nickel sulfamate solutions, such as those commonly used in the electro deposition of nickel, by dissolving nickel oxide or nickel carbonate in aqueous solutions of sulfamic acid. The economics of these procedures is adversely afiected by the fact that nickel oxide and nickel carbonate of desired purity are generally not available except at premium prices. Accordingly, methods have long been sought whereby nickel sulfamate solutions can be produce rapidly and efiiciently using readily available and standard priced nickel source material. Since high purity nickel powder is commercially available at standard nickel prices, its use as a nickel source for electroplating solutions is very attractive from an economic point of view. However, problems are encountered in using nickel powder as a nickel source for nickel sulfamate solutions which, prior to the present invention, have prevented its widespread use for this purpose.

Two serious problems in this regard are the slow rate of dissolution of nickel powder in aqueous sulfamic acid solution and the tendency of the sulfamic acid and nickel sulfamate to hydrolyze whereby reagents are wasted and the nickel sulfamate solution is contaminated with sulfate ions. The rate of dissolution can be increased by increasing the temperature of the solution but the problem of hydrolysis is aggravated at higher temperatures.

It is the principal object of the present invention to provide a method for rapidly producing nickel sulfamate using nickel powders as the nickel source material.

Another object of the invention is to provide a method for rapidly dissolving nickel powder in aqueous sulfamic acid solutions with minimum hydrolysis of nickel sulfamate and sulfamic acid.

A further object of this invention is to provide an efficient, inexpensive method of producing aqueous nickel sulfamate solutions from standard priced nickel powders.

A still further object of this invention is to provide a method for rapidly producing substantially iron-free nickel sulfamate from nickel powders containing iron as a contaminate.

Other objects and a fuller understanding of the invention may be had by referring to the following description and claims taken in conjunction with the accompanying drawings in which:

FIG. 1 is a graph showing comparative dissolution rates for nickel powder in sulfamic acid with oxygenation aeration and simple agitation;

FIG. 2 is a graph showing comparative dissolution rates for nickel oxide in sulfamic acid in accordance with conventional practice and for nickel powder in sulfamic acid in accordance with the method of the invention; and

FIG. 3 is a graph showing the effect of oxygen enrichment of air on the nickel dissolution rate.

The present invention is based on the discovery that a remarkably fast dissolution ate for nickel powder in aqueous sulfamic acid solution can be obtained by oxygenating a sulfamic acid solution-nickel powder suspension containing at least the stoichiometric amount of nickel required to combine with the sulfamic acid as nickel sulfamate. Further, we have found that the rapid dissolution rate obtained by oxygenation of the suspension together with the controlled addition of sulfamic acid to maintain the pH below about 5.0, eliminates hydrolysis of sulfamic acid and nickel sulfamate or at least reduces it to acceptable levels. Nickel dissolution rates are further substantially enhanced by active agitation, conducting the reaction at slightly elevated temperatures up to about 65 C., providing nickel in excess of that required to combine with available sulfamic acid, and by providing oxygen in excess of that actually consumed in the dissolution reaction.

in carrying out the method of the present invention, nickel powder is suspended in water which may or may not contain some free sulfamic acid, and the acid required to produce the desired nickel sulfamate concentration in the final solution is added to the slurry in the manner described in detail hereinbelow. The nickel-acid slurry is agitated to maintain the nickel particles in suspension and is oxygenated until the reaction of the sulfamic acid with the nickel is substantially complete. Thisdissolution step may be carried out in any conventional equipment having the required corrosion resistance and provided with suitable agitator means for maintaining the nickel in suspension and provided with means for feeding oxygen into the solution in the manner discussed in more detail hereinbelow. The nickel sulfamate solution is then separated from the undissolved nickel particles, such as by decantation, and the cycle is repeated with the addition of fresh process water, nickel powder and sulfamic acid.

Generally speaking, the method is independent of the source of the nickel powder used as a starting material. That is, the powder can be produced by conventional pyrometallurgical or hydrometallurgical processes. The powder may contain minor amounts, in the order of 0.2 percent or less, of metallic impurities normally found in association with nickel such as cobalt, iron and copper, for example. Other impurities such as carbon and sulfur may also be present in minor amounm. We have found that nickel powder produced by precipitation from a solution in which it is present as a salt by reacting the solution with a reducing gas at elevated temperature and pressure is particularly suitable. Powders obtained by this method are characterized by their high purity, generally at least 99.8 percent nickel, and are obtainable in controlled sizes ranging from submicron to about 300 microns. Nickel powders within the size range of 40 to microns (which is the size distribution of the standard grade commercial powders produced by this method) are satisfactory although faster dissolution rates will be obtained with even finer powders since the reaction rate increases with decreasing powder size.

The amount of nickel maintained in suspension in the solution must be at least the stoichiometric amount required to combine with the available sulfamic acid to fonn nickel sulfamate. it is preferred, however, especially when coarser powders are employed, to provide nickel in substantial excess of the stoichiometric requirements of the sulfamic acid as the nickel dissolution rate is enhanced by the presence of excess nickel. Having regard to various operating factors, three to five times the stoichiometric requirements is generally satisfactory, although the method can be operated with up to 10 times or more stoichiometric.

The total amount of sulfamic acid provided is that required to combine with available nickel to produce the desired nickel sulfamate concentration in the final solution. An important feature of the invention is the control of the sulfamic acid addition to maintain the pH within a range in which hydrolysis of sulfamic acid and nickel sulfamate is minimized. it is preferred to add the sulfamic acid to the nickel-water slurry in solid form as the dissolution reaction progresses at a rate which will maintain the pH of the system below about 5.0 and preferably in the range of 1.5 to 2.5. The dissolution reaction is accelerated by oxygenating the suspension, preferably by sparging with substantially pure oxygen gas, and by active agitation to maintain the nickel particles in suspension. Once the total acid requirements have been added, the reaction is continued with active agitation and oxygenation until the nickel-sulfamic acid reaction is substantially complete. The completion of the reaction is indicated by an abrupt rise in the pH. Generally, a cycle is terminated when the pH reaches about 5.0.

Thorough oxygenation of the nickel-acid suspension is an essential requirement for obtaining the rapid dissolution of the nickel powder in the sulfamic acid in accordance with this invention. it is preferred to oxygenate the system by feeding substantially pure oxygen gas into the solution through subsurface spargers or the like. The spargers employed for this purpose preferably consist of conduits adapted to feed fine gas bubbles into the solution at or near the bottom of the reaction vessel. The spargers should be configured and positioned to ensure maximum dissemination of oxygen throughout the solution.

it is believed that the dissolution of nickel powder in aqueous sulfamic acid, in the presence of oxygen proceeds according to:

Ni-+2HSO,NH,+%O, Ni( SO,NH, ),+H,O According y, th minimum amount of oxygen that must be provided in accordance with this invention is that required to satisfy the above equation. in practice, the amount of oxygen required will always be higher because of the mass transfer phenomenon and the losses occurring from an open vessel. In general, it is preferred to supply from about 1.1 to about 1.5 times the theoretical oxygen requirements. Some increase in dissolution rate can be achieved by providing the oxygen requirements by aeration. However, we have found that oxygenation with substantially pure oxygen gas is as much as five times as effective as air in accelerating the rate of dissolution of the nickel. Apparently, nitrogen has a passivating efi'ect on the nickel particles; thus its presence in even minor amounts is deleterious to the dissolution rate. Oxygen enrichment of the air will not overcome the passivating efiect of the nitrogen until the air is enriched with at least 90 percent oxygen. This phenomenon is illustrated graphically in FIG. 3. It can be observed that the dissolution rate of the nickel powder in the sulfamic acid solution remained essentially constant as the oxygen content of the air was increased until oxygen content reached about 90 percent. At this point, there was an abrupt increase in dissolution rate, as indicated by the steep slope of the curve and 100 percent dissolution was achieved in a very short period.

The method of this invention therefore contemplates the use of pure oxygen gas or oxygen gas containing no more than percent air for oxygenation of the nickel-acid suspension. The expression substantially pure oxygen gas as used herein is intended to include oxygen gas containing up to 10 percent air or other nonoxidizing gases which do not adversely afiect the dissolution reaction, and the term oxygenation as used herein means treatment with substantially pure oxygen gas.

Using active agitation and oxygenation, a relatively rapid dissolution rate is obtained at room temperature. However, the dissolution rate can be considerably enhanced by conducting the reaction at an elevated temperature below about 65 C. For example, in producing a solution containing about 160 g.p.l. of nickel as nickel sulfamate, temperature afiects nickel dissolution rate as follows: dissolution time is decreased from 120 minutes at room temperature to 110 minutes at 40 C. to 80 minutes at 60 C. Higher temperatures are permissible but the danger of hydrolysis of the sulfamic acid increases with increasing temperature. The preferred range for carrying out the process is about 40 C. to about 60 C.

As noted above, the nickel powder dissolution reaction is conducted at a pH below 5.0 and preferably in the range of about 1.5 to about 2.5. The control of solution pH is necessary in order to minimize hydrolysis which would result in the wasting of reagents and contamination of the solution with sulfate ion. The pH can be conveniently controlled in the desired range by controlling the rate of addition of sulfamic acid to the slurry. Once the total acid requirements have been added and the reaction carried to completion with active agitation and oxygen sparging, the cycle is terminated and the unreacted nickel particles are allowed to settle. The nickel sulfamate solution is then decanted and, if necessary, is subjected to further oxygenation or aeration to effect precipitation of iron. The clarified solution can be used directly in electroplating applications, for example, or it can be evaporated to produce solid nickel sulfamate. The unreacted powder from a preceding cycle is equally as reactive as fresh powder and there is no serious buildup of impurities where the powder initially is of high purity. Any iron contamination derived from the nickel powder can be readily removed from the nickel sulfamate solution by continued oxygenation for a period of time after the reaction between the sulfamic acid and the nickel is complete. By this procedure, ferrous iron is oxidized to ferric iron which precipitates from solution as an insoluble compound. In order to avoid a buildup of iron contamination in the reaction vessel, the preferred procedure is to continue the oxygenation or aeration for the removal of the iron afier the solution has been separated from the undissolved nickel.

The invention is further illustrated and explained by the following examples. In these examples, nickel powder obtained by hydrogen reduction from an aqueous ammonia-ammonium sulfate nickel solution was utilized. The chemical and physical characteristics of this powder were as follows:

Chemical analysis Ni Balance Screen analysis (Standard Tyler Mesh) Apparent Density 4.47 grams per cc.

EXAMPLE 1 Four hundred grams of the above described nickel powder were slurried in 1 liter of water in a 2 liter glass beaker equipped with stainless steel (316) baffles, 30 mm. fritted glass spargers, and pencil-type immersion heaters. The nickel powder was maintained in suspension by mechanical agitation and the slurry sparged with oxygen gas supplied at a rate of 0.25 liter per minute. 264.3 grams of sulfamic acid in solid form were added at a uniform rate sufiicient to maintain the pH of the system of about 1.5. The temperature during the experiment varied between 30 C. and 60 C. After all the sulfamic acid had been added, the agitation and oxygen sparging were continued until substantially all of the free sulfamic acid had reacted and the pH of the solution reached about 5. The total time required to reach this point was 33 minutes and the solution, after separation from the undissolved nickel particles, analyzed (g.p.l.) 77.2 Ni, 0.004 Fe, 0.07 42.9 NH The final pH was 5.7.

EXAMPLE 2 The procedure of example 1 was followed except that 800 g. of nickel powder were slurried with 1 liter of water, 528.6 g. of solid sulfamic acid were added, and the slurry was sparged with oxygen supplied at the rate of 0.35 liter/min. (1.18

stoichiometric). The dissolution was complete in 103 minutes and the solution analyzed: (g.p.l.) X1693 Ni, 0.023 Fe, 0.14 80, and had a pH of 5.0.

Examples 1 and 2 demonstrate that nickel sulfamate solutions can be produced in remarkably short periods using oxygenation in accordance with the method of the present invention. The improved results obtainable by the method of the invention are further shown in FIGS. 1 and 2 of the accompanying drawings. FIG. 1 is graphically shows comparative dissolution rate for the nickel powder employed in examples 1 and 2,A--with oxygenation in accordance with the method of the present invention, B-with active agitation and aeration, and C-with active agitation but neither oxygenation nor aeration. In each case, 264 g.p.l. of sulfamic acid and 400 g.p.l. of nickel powder (fivefold excess over stoichiometric) were used. The greatly improved dissolution rate for nickel powder in sulfamic acid obtainable by the method of this invention is readily apparent. FIG. 2 graphically shows comparative dissolution rates for Anicltel powder in sulfamic acid according to the method and B-nickel oxide in sulfamic acid in accordance with conventional methods. Curve A was plotted from data obtained by following the procedure of example 1 except that 260 g.p.l. sulfamic acid were used together with 80 g.p.l. of very fine (98 percent 325 mesh) powder obtained by hydrogen reduction from an aqueous ammoniated nickel carbonate system. Curve B was plotted from data obtained by dissolving l08 g.p.l. of very fine (98 percent 325 mesh) nickel oxide in a solution containing 260 g.p.l. sulfarnic acid.

EXAMPLE 3 This example illustrates the influence of excess nickel powder on the production of nickel sulfamate solutions using oxygen sparging. A series of experiments were conducted following the procedure of examples 1 and 2 except that in each experiment the amount of excess nickel powder was diminished. The results are shown in table 1.

TABLE 1 the latter being employed for certain intervals only during the reaction (for example towards the end of the dissolution period) to speed up the reaction and reduce the overall operating time and to provide a degree of flexibility in the productivity of the unit.

Nickel powder added Chemical analysis, g.p.l.

Final pH alter fil- Ni Fe S04 tration 75. 2 0. 004 0. 07 6 73. 0 0. 002 0. 08 6. 4 73. 4 0. 004 0. 10 6. 1 75. 2 0. 004 0. 14 6. 1 68. 2 0.017 0. 31 1. 7 138 0. 012 0. l0 5. 7 141 0. 006 0. ll 5. 5 150 0. 013 0. 15 5. 7 172 0. 002 0. 5. 7

The method of this invention possesses a number of important advantages over the prior art methods for preparing nickel sulfamate. Firstly, it permits the utilization of standardpriced nickel source material and, at the same time, drastically reduces the time required to effect the conversion of the starting material to nickel sulfamate. The resulting improvement in the economics of the process will be self-evident. in addition, the method provides a umber of important operating advantages including elimination of dust and improved filtration characteristics resulting from the rapid settling characteristics of nickel powder.

It is to be understood that oxygenation with substantially pure oxygen in accordance with the present method may be used in whole or in part in any overall process for producing nickel sulfamate by dissolution of nickel powder in sulfamic acid solution. For example, it may be advantageous to use both aeration and oxygenation during the dissolution reaction,

tion of iron contaminated nickel powder in aqueous sulfamic solution which comprises forming a suspension of finely divided nickel in water, adding sulfamic acid to said suspension to provide a total amount of sulfamic acid up to the stoichiometric amount required to combine with all nickel present as nickel sulfamate, controlling the rate of addition of sulfamic acid to maintain the pH of the suspension in the range of about 1.5 to about 5.0, feeding a gas mixture consisting essentially of oxygen and no more than about l0 percent air into the suspension, continuing the dissolution reaction at a temperature below about 65 C. with active agitation and treatment with said gas until substantially all free sulfamic acid is reacted, withdrawing iron contaminated nickel sulfamate solution and subjecting said last-mentioned solution to further treatment with oxygen to remove iron contamination by precipitation of dissolved iron as an insoluble compound.

i i l i I 

